AME 14:39-48 (1998)  -  doi:10.3354/ame014039

Major and comparable roles for free-living and attached bacteria in the degradation of Phaeocystis-derived organic matter in Belgian coastal waters of the North Sea

S. Becquevort*, V. Rousseau, C. Lancelot

Groupe de Microbiologie des Milieux Aquatiques, Université Libre de Bruxelles, Campus de la Plaine, CP 221, Boulevard du Triomphe, B-1050 Brussels, Belgium

Microbial degradation of Phaeocystisglobosa colonies and their derived organic matter by free-living and attached bacteria was investigated in Belgian coastal waters during the spring development of diatom-Phaeocystis colonies in 1994. Results obtained show concomitant evolution of hydrolytic ectoprotease and b-ectoglucosidase ectoenzymatic activities with respect to the phytoplankton bloom, suggesting that the low biodegradability of Phaeocystis colonies leading to transient accumulations of Phaeocystis-derived material in the coastal North Sea was not due to a lag phase required for the induction of b-ectoglucosidase. Up to 66% of total bacterial biomass was found attached to particles larger than 10 μm. While occurring always in low abundance compared to free-living bacteria, both the average specific biomass and growth rate of particle-attached bacteria were very high, i.e. 60 fg C cell-1 and 0.28 h-1, respectively. Similarly, specific ectoenzymatic activities of particle-attached bacteria were on average about 5 times higher than those characterising free-living bacteria. Budget calculations show a 53% contribution of Phaeocystis-attached bacteria to the mineralisation of Phaeocystis-associated production, i.e. a 53:47% role for attached and free-living bacteria, respectively.


Phaeocystis degradation · Free-living and particle-attached bacteria · Ectoenzymatic activity · Growth rate


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